1. Field of the Invention
The present invention relates to a liquid droplet discharge head and an image forming apparatus including the same.
2. Description of the Related Art
As an image forming apparatus such as a printer, a facsimile machine, a copier, a plotter, or a multifunction apparatus combining several of the capabilities of the above devices, for example, an inkjet recording apparatus is known which includes an ink droplet discharge head to discharge ink droplets and form images on a medium while conveying the medium by adhering the ink droplets to, for example, a sheet of paper or the like.
The inkjet recording apparatus includes nozzles to discharge ink droplets, a pressurized chamber communicating with the nozzles, an actuator to generate energy to increase the pressure inside the pressurized chamber, and a common liquid chamber communicating with the pressurized chamber and supply ink to the recording head. By activating the actuator, the pressure in the pressurized chamber is increased, thereby expelling ink droplets from the nozzles.
Inkjet recording apparatuses including a piezoelectric actuator are widely available, in which the actuator for discharging ink droplets is embodied as a piezoelectric actuator which vibrates in a direction perpendicular to an axial direction of a piezoelectric element. In such an inkjet recording apparatus using the piezoelectric actuator, drive pulse voltage generated by a drive voltage generator is applied to the piezoelectric elements fixed on a diaphragm which forms a part of an inner wall of the pressurized chamber, and the piezoelectric element vibrates. Due to the vibration of the piezoelectric element, the diaphragm displaces, thereby changing the inner pressure of the pressurized chamber. With this structure, the ink inside the pressurized chamber is discharged from nozzles as ink droplets as the ink is being supplied from the common liquid chamber to the pressurized chamber.
In the recording head of such an inkjet recording apparatus, because the ink is discharged from the nozzles onto a sheet to form an image, the ink is exposed to the atmosphere, which causes a solvent included in the ink to evaporate. As a result, agglomeration of the ink increases and the agglomerated ink tends to clog in nozzles, thereby causing defective ink discharge.
Japanese Patent No. 3611177 (JP-3611177-B) discloses a method of preventing defective discharge due to agglomerated ink inside the recording head. The disclosed method includes the following steps: (1) Based on the print data, operation status for each nozzle is analyzed before printing. Operation status includes data to show when and where each nozzle discharges ink droplets. (2) Pulse voltage being a constant peak voltage for micro-driving is applied to the piezoelectric element responsive to the analyzed operation status of each nozzle. The micro-driving means applying pressure of such a degree as not allowing the ink to be discharged from the nozzle by applying a pulse voltage for micro-driving with a peak voltage less than the peak voltage of the pulse voltage for normal driving, to the ink inside the recording head. The pulse voltage for the micro-driving is generated by voltage generator for the micro-driving. According to this, meniscus formed in the nozzle is slightly vibrated so that the viscous ink inside the recording head is agitated, thereby improving the viscosity degree of the viscous ink.
The method disclosed by Japanese Patent No. 3611177, however, has a disadvantage in that, due to repeated and long-time application of the pulse voltage to the piezoelectric element, the viscous ink diffuses inside the pressurized chamber and the volume of the liquid ink including the viscous ink is increased. As a result, the amount discharged by the dummy discharge for maintaining the discharging performance increases, resulting in unnecessary consumption of the liquid ink.